Modern jet transports are equipped with a cockpit panel that interfaces with a flight management system to control the selection and engagement of automatic flight control modes of operation. The panel is usually mounted on the glare shield within easy reach of both pilots and is given various names such as "mode control panel," "mode select panel," "flight control unit," etc. The panel provides an interface between the pilot and the flight management system, which controls the autopilot/authothrottle systems of the airplane. The panel is used by the pilots to select the vertical and lateral flight control modes desired, which selection supercedes pre-existing and/or default modes. The vertical mode is used to control the airplane's speed (by controlling enginer thrust and airplane attitude) and altitude between takeoff and landing. Typically, a pilot selects the thrust rating of the engines and a desired vertical speed for the initial climb after takeoff. Next, the pilot typically sets thrust at the rating level of the engines and speed at a desired climb speed for the enroute climb to cruise altitude. When cruise altitude is reached, speed is set based on some established criteria (most economical, shortest elapsed time, etc.) consistent with maintaining the cruise altitude. During descent, typically, the pilot sets the engines to their idle thrust rating and selects a descent speed designed to achieve the desired descent profile. The lateral mode is used by the pilot to select any one of various options. It may be used to select a particular heading, which would result in the airplane's flight path changing to a selected heading. Alternatively, the present heading may be maintained by a heading hold selection. Or, automatic navigation, which tracks a preprogrammed route using steering signals from an inertial or area navigation system, may be selected.
More recent flight management systems have been enhanced by the addition of more sophisticated automatic flight control modes of operation. These include flight level change (FLCH), vertical navigation (VNAV) and lateral navigation (LNAV) flight control modes of operation. The FLCH mode automatically manages thrust and speed to climb or descend from one altitude to another. The VNAV mode provides automatic optimized profile control from initial climb through final approach, including adherence to terminal area procedure speed and altitude constraints. The LNAV mode provides automatic steering to a preprogrammed route including selected terminal automatic flight control araea procedures.
Regardless of the sophistication of the modes of operation, in all flight management systems, the pilot chooses the available modes that will best accomplish the desired vertical flight profile and lateral routeing. In most instances, the pilot plans the flight in advance, both laterally and vertically, and preprograms the LNAV and VNAV modes so that the desired flight path will be followed. While preprogrammed flights are advantageous because they reduce the pilot's burden, particularly during takeoff and landing, in practice, rarely can flights be flown as preplanned. Usually, rerouting an reclearances instructions are received from air traffic control (ATC) during the flight. These instructions force the pilot to depart from the vertical flight profile and/or the lateral route that was originally planned. In some instances, rerouting and reclearance come far enough in advance to allow the pilot to reprogram the route or profile instructions stored in the memory of a flight management computer so that the flight management system can remain in the LNAV and VNAV flight control modes. On other occasions, pilots are forced to depart from LNAV and VNAV modes in order to comply with ATC instructions in a timely manner. Unfortunately, this often occurs when the ATC instructions cannot be conveniently accommodated either due to crew workload or system capability.
When a pilot is required to depart from LNAV or VNAV modes of operation in order to comply with ATC rerouting or reclearance instructions, the pilot must determine and select the alternate modes of operation which best fit the instruction. For example, if a pilot is radar vectored off of a preplanned route during descent, the pilot would like to be able to select a heading that will automatically capture and track the clearance heading once the radar vector constraint is lifted. If the pilot is vectored far enough off the preplanned route, such that the original route is entirely invalidated, the pilot may want to substitute vertical speed control for the preprogrammed VNAV control and select an autothrottle speed or set thrust at idle. When this occurs, what starts as a straight-forward heading clearance change expands into a multi-axis control problem. Although pilots cope with situations resulting from ATC rerouting and reclearances, such coping has a number of disadvantages. Pilot workload is often increased as a result of such changes at a time when it should be decreased. Flight optimization is sacrificed. In some cases there is a tendency on the part of pilots to try to reprogram the route/profile instructions stored in the flight management computer when pilot attention should be focused on flight progress.
The invention is directed to overcoming the foregoing problems by providing an intervention flight management system that allows a pilot to intervene in the operation of the preprogrammed flight management computer of a flight management system and change the speed and/or flight path of an airplane in response to air traffic control instructions.